A technique that can amplify weak optical signals, while simultaneously reducing noise has been developed by researchers in Canada. By exploiting the Talbot effect, the team showed how arbitrarily-shaped signals can be reliably detected, even when buried in background noise. The research was led by José Azaña and Benjamin Crockett at Quebec’s National Institute of Scientific Research.
The ability to detect weak, noisy optical signals is important in many aspects of science and technology. These include long-range telecommunications, where signals are weakened as they propagate through optical fibres; and biomedical imaging, where weak light beams are necessary to avoid damage to delicate living tissues.
Weak signals can be enhanced using active amplification, but this worsens the signal to noise ratio. Passive methods such as filtering-out noise tend to also attenuate the signal of interest, and do not work for signal bandwidths narrower than a few gigahertz.
Self-imaging effect
To address these problems, Azaña’s team turned to a passive amplification technique derived from the Talbot self-imaging effect, which occurs when light passes through an optical grating. It is a diffraction effect that can be used to combine successive light pulses by “stacking” them on top of each other – creating more powerful pulses. So far, however, this technique has been incompatible with the non-periodic, arbitrary waveforms found in most practical optical signals.
Building on previous work, Azaña and colleagues used a more advanced form of the Talbot set-up to passively redistribute the energy of a weak signal into a high-intensity pulse. Crucially, this could be done without distorting the waveforms of the signals. The technique also reduced the overall signal-to-noise ratio. This enabled the researchers to amplify non-periodic signals by a factor of more than 100, while reducing relative noise in the measured signal.
Such a powerful approach could allow light sensors to pick up optical signals well below their current detection thresholds – signals that are buried deep within a noisy background. Furthermore, the technique is compatible with bandwidths spanning several orders of magnitude, from kilohertz to gigahertz. This enabled the team to amplify a diverse range of technologically relevant optical signals from ultranarrowband waveforms to broadband signals.
Azaña’s team envisage a wide array of potential applications for their approach. They hope that it could be adapted to convey 2D and 3D images – with promising potential uses in fields including astronomy, photography and holography. With further improvements, their Talbot-effect concept could also be adapted to amplify noisy signals carried by other wave types. These may include additional electromagnetic wavelengths, sound and potentially even quantum matter waves.
Researchers in Norway and Germany have shown that structural colouration can be easily created from clay suspensions. Due to the sustainability and abundance of clay minerals, this could lead to inexpensive structural colours that are environmentally friendly and non-toxic, with applications ranging from cosmetics and health to windows and tiles, they claim.
Most colours are created by the absorption of light by dyes and pigments. The colours we see are the wavelengths that are not absorbed and bounce back. Structural colours are different. They are produced by nanostructures that scatter and reflect light. Scientists are interested in creating structural colours as they could be more sustainable and durable than colours from dyes and pigments.
Due to the natural abundance, stability and low toxicity of clays, Jon Otto Fossum, a physicist at the Norwegian University of Science and Technology, and his colleagues wanted to see if they could be used to create structural colours. They started their research using the synthetic clay Na-fluorohectorite. When immersed in water, Na-fluorohectorite forms liquid crystal suspensions with single nanosheets of the mineral separated at a uniform distance from each other. This distance is linked to the concentration of the suspension – the ratio of water to Na-fluorohectorite.
In their latest work, reported in Science Advances, the researchers demonstrate that the clay particles in these semi-transparent suspensions reflect light and produce colour. By adjusting the Na-fluorohectorite-to-water ratio, and therefore the distance between the nanosheets, they were able to tune the wavelengths of light reflected and the colours produced. While this generated colours covering the whole spectrum, they were not particularly bright.
To increase the brightness, the team turned to an interstratified – alternate layered – mixture of Na-fluorohectorite and caesium. When emersed in water, the Na-fluorohectorite again separated into nanosheets, but this time they formed double layers bound together by a thin layer of caesium. This quickly produced structural colouration that was much brighter than with the single sheets of Na-fluorohectorite, as the thicker double layers reflect more light.
“We can make clay nanosheets less transparent by making and using a double nanothin layer with an element between them,” says Fossum. “In this example, we used the element caesium, but other substances can also be used.”
The structural colours could be rapidly tuned by adding more water, the team found. The nanosheet spacing is controlled by electrostatic interactions, so it can also be changed by adjusting the ionic strength of the solution. When the researchers increased the salt concentration of a red double layer suspension, the colour shifted through yellow and green to blue. The increasing salt levels dampened the electrostatic forces between the layers and the separation distance decreased.
“The distance between the double clay layers is what produces the colour we see,” Fossum explains. “We can control that distance by means of the clay concentration or salt content in the material, such as water, that the clay is suspended in.”
According to the researchers, the technique should also work with natural clays, such as vermiculite. They note that the clay can be suspended in other transparent materials besides water, including polymers or hydrogel matrices. Here, the clay nanosheets could provide additional benefits as they are known to improve the mechanical strength and stability of such materials. This could enable the development of composites from normally mechanically weak matrices with tunable structural colouration, mechanical strength and stability, the researchers claim.
Next, Fossum and his colleagues plan to test different matrices such as biobased polymers to create sustainable and biodegradable pigments. They add that by using responsive polymers they may also be able to create colours that can be changed by applying electric, magnetic or mechanical forces.
Two independent teams of researchers in the US have used differential measurement techniques to remove laser noise from atomic clocks. This allowed one team to observe tiny differences in how gravity affects atoms separated by less than 1 cm in height. One of the teams hopes that its practical technique could allow atomic clocks to be used more widely in applications such as geodesy and gravitational wave detection. The second group is the first to demonstrate that time runs slower at the bottom of a millimetre-sized atomic ensemble than it does at the top – further confirming a prediction of Einstein’s general theory of relativity.
Atomic clocks are the most precise timekeeping devices invented so far. They work by using the frequency of an extremely narrow transition in an atom or ion as a reference standard for the frequency of a laser. The best atomic clocks are so stable that they would be out by less than one second after running for the age of the universe.
This precision allows for astonishing experiments to be done. In 2018, for example, researchers at the US National Institute for Standards and Technology (NIST) in Boulder, Colorado compared the frequencies of two state-of-the-art clocks comprising ytterbium atoms trapped in optical lattices. This comparison was done at a precision of about 1 part in 1018, which is good enough to detect the tiny difference in the frequencies of two clocks when one clock is just 1 cm higher in elevation than the other.
Gravitational time dilation
This frequency difference occurs because the lower clock is slightly closer to the centre of the Earth and therefore experiences a slightly larger acceleration due to Earth’s gravity than the upper clock. This causes the lower clock to run slower than the upper clock – an effect called gravitational time dilation, which is predicted by general relativity.
The ability to make such measurements outside the lab could lead to “relativistic geodesy”, whereby atomic clocks provide extremely precise information about Earth’s shape, interior and gravitational field. Other potential applications include gravitational wave detection, which could involve putting high-performance atomic clocks in space. However, today’s best atomic clocks are extraordinarily precise scientific instruments, and taking them outside the lab without sacrificing stability is not currently possible.
One team reporting new results is led by Shimon Kolkowitz of University of Wisconsin-Madison. It has taken an important step towards solving this stability problem by trapping two ensembles of strontium atoms at different elevations in the same vertical 1D optical lattice. The team addressed each ensemble with the same, commercially available laser. Both ensembles were subject to the same laser noise – which was relatively large compared to the state-of-the-art devices created at NIST.
Kolkowitz points out that “you can’t use [our system] as a traditional clock…We don’t learn about the absolute frequency, but we do know that it’s the same for both ensembles”.
Equally affected by noise
Crucially, tiny differences in the behaviours of the two ensembles could be measured because the laser noise affected both equally. The researchers achieved a relative uncertainty in their difference measurements of less than 1 part in 1019. However, because of other experimental factors, they were not able to observe gravitational time dilation.
Kolkowitz and colleagues went on to develop networks of clocks in their optical lattice comprising six ensembles of atoms. They were also able to use different isotopes of strontium in each ensemble. This could be useful in the search for deviations from the Standard Model of particle physics, explains Kolkowitz, “You’d really like to learn about the difference in the clock transition for two different isotopes of strontium”. He adds, “There are proposals for using those measurements to search for new particles and new forces,” and points out that Vladan Vuletic at the Massachusetts Institute of Technology has done measurements using different atoms.
Meanwhile, Jun Ye and colleagues at the Joint Astrophysical Laboratory (JILA) – operated by NIST and the University of Colorado – did a similar experiment using an existing strontium optical clock that is one of the most stable in the world. They were able to achieve a relative uncertainty of less than 1 part in 1020 when comparing strontium atoms within an optically-trapped ensemble that was just 1 mm in height. Ye says, “We plotted a linear slope of the time dilation as a function of the vertical distance” – an effect that is predicted by general relativity.
Very high fidelity
“We still took advantage of laser noise being differentially removed,” explains Ye, “but the laser quality played an important role in our experiment in the sense that the state preparation was extremely clean and very high fidelity”.
The JILA team hopes to improve their technique even further so that they can study the effects of gravity on macroscopic quantum states. “I don’t think we’re at the scale of being able to talk about quantum gravity,” Ye says. “In quantum gravity, the concept of time itself becomes multi-dimensional and discontinuous. However, [future work] will probably bring general relativity to meet with the microscopic world and shed light on quantum decoherence by gravity.”
Both groups describe their research in separate papers in Nature.
“These are beautiful papers,” says atomic physicist Christian Lisdat of the German National Metrology Institute. “It’s really impressive to see how they use the capabilities we have to manipulate and investigate atoms to circumvent some of the problems we are facing and to get better measurement capabilities.”
“I think they’re very, very nice advances along two different fronts,” says Vuletic. “Kolkowitz’s paper has this new technology to make multiple ensembles, which is great: it’s maybe less impressive along the axis of the development of accurate clocks but it’s more a field-opening paper. Ye’s paper is at the absolute precision frontier, and this ability to measure gravitational redshift over millimetres is just amazing.”
Correction: the original version of this article suggested incorrectly that Kolkowitz and colleagues had observed gravitational time dilation.
With the Winter Olympics ending this weekend, I couldn’t resist this story about simulated slapshots. The slapshot is the most difficult shot in ice hockey and it is all about power and speed. Indeed, the fastest slapshot puck was clocked at a blistering 175 km/h.
To do a slapshot, the player draws back their stick and then accelerates it down and forward, so the blade slaps the ice just behind the puck. As the stick strikes the ice it flexes, storing energy that is released when it reaches the puck.
In the 19th century hockey sticks were made from a solid piece of wood, but they broke easily. Players started using much stronger laminated wooden sticks, which made the slapshot possible. Fast forward to 2000, and players started using sticks made from composite materials that are even stronger and lighter than wood – so slapshot speeds increased.
Dynamic loading
Now, scientists at US-based Altair Engineering have used the company’s Radioss dynamic loading simulation to understand why composite materials offer hockey players an advantage. They found that a composite stick gives a higher degree of control over the puck when compared to a wooden stick. This allows more energy to be delivered to the puck from a composite stick. You can read more about the study here and watch the simulations.
A good hockey player has an intuitive understanding of how to make a slapshot, in the same way that a good crane operator knows how to shift a load while preventing it from swinging back and forth. Cranes that operate on construction sites lift loads using a long cable. As a result, the load is a pendulum that has a natural frequency of oscillation. When the load starts to move horizontally, it will naturally start to swing back and forth – but a good operator will know the tricks required to dampen the motion.
Now, the physicist Stephan Schlamminger at NIST in the US has stumbled upon these tricks while he was developing ways to control the motion of torsion pendulums. These pendulums are used to make extremely precise measurements of the gravitational constant.
As Schlamminger was developing his equations he recalled a conversation he had many years ago with a fellow physicist who told him about the tricks that crane operators use to control their loads. He realized that he could adapt his equations to apply to cranes and has published a paper describing his findings. You can read more about his research here and also watch a video demonstration.
Photoplethysmography is a non-invasive, optical measurement technique that is widely used for health monitoring. Much research focuses on how to leverage the wealth of information in the photoplethysmogram (PPG) signal, and how to use this information to inform clinical decisions.
This webinar will feature talks from leaders in the field, on topics ranging from using photoplethysmography for cardiovascular risk assessment, for cuffless blood pressure monitoring, and validating these technologies for clinical use. It will provide insight into the state-of-the-art and key directions for future research.
Left to right: Xiao Hu, Pete Charlton, Rich Fletcher, Raquel Bailón Luesma, Ramakrishna Mukkamala and Xiaoman Xing.
Chair Xiao Hu, Editor-in-chief, Physiological Measurement, Emory University, USA.
Organizer Pete Charlton, Board member, Physiological Measurement, University of Cambridge, UK.
Speakers Rich Fletcher, Massachusetts Institute of Technology, USA. Rich presently directs the Mobile Technology Group in the MIT Mechanical Engineering Department. His research utilizes a variety of mobile technologies, wearable sensors, and Internet of Things for behaviour monitoring, in addition to psychological and behavioural interventions.
Raquel Bailón Luesma, University of Zaragoza, Spain. Raquel is an associate professor at the University of Zaragoza, Spain, within the Department of Electronic Engineering and Communications. Her current research interests include the biomedical signal processing field, especially in the analysis of the dynamics and interactions of cardiovascular signals.
Ramakrishna Mukkamala, University of Pittsburgh, USA. Ramakrishna is a professor in the Departments of Bioengineering and Anesthesiology and Perioperative Medicine at the University of Pittsburgh. His primary research interests are in cardiovascular monitoring.
Xiaoman Xing, Suzhou Institute of Biomedical Engineering and Technology, China. Xiaoman is a professor at Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences. Her research interests include biomedical signal processing, cardiovascular physiology, sleep medicine, mental health, and patient monitoring.
Physiological Measurement covers the quantitative measurement and visualization of physiological structure and function in clinical research and practice, with an emphasis on the development of new methods of measurement and their validation.
Artificial intelligence (AI) can help radiologists lessen their workload when reading digital breast tomosynthesis (DBT) images by nearly 40%, according to research published in Radiology.
A team led by Yoel Shoshan and Ran Bakalo from the University of Haifa in Israel developed an AI model that they say can filter out cancer-free cases and keep up with radiologists in terms of accuracy.
“Because 99.5% of screening examinations are cancer free, deploying such an AI system to optimize screening reads could be of substantial value,” the group write.
The use of DBT is expected to grow worldwide, with previous research showing its ability to improve cancer detection and improve recall rate over conventional mammography. However, one downside to using DBT is it requires about twice the interpretation time as mammography, the researchers note. This means more work for radiologists and higher costs for screening programmes.
Previous research also suggests that AI can help save time and reduce workload for breast radiologists. Shoshan, Bakalo and colleagues wanted to test the ability of their AI model to filter out normal DBT studies to reduce screening workload while improving diagnostic accuracy.
Screening workflow: the team examined whether AI could reduce radiologists’ workload by filtering out a portion of the cancer-free examinations. (Courtesy: CC BY 4.0/Radiology 10.1148/radiol.211105)
The team developed the model by training it in a cohort of 9919 women with a total of 13,306 DBT exams. This was split into a training set of 3948 women (804 cancers), a validation set of 1661 women (182 cancers) and a test set of 4310 women (453 cancers).
For the study, the researchers used the test set of data, which included a total of 5182 DBT examinations performed between 2013 and 2018. The women in the test set had an average age of 60 years. The model was also used in a simulated workflow where it classified cancer-free examinations that could be dismissed from the screening worklist.
The model reduced screening workload by 39.6% with a sensitivity of 90.0%, while the radiologists had a sensitivity of 90.8% (p < 0.001), the researchers found. The model also filtered out cancer-free examinations, which led to a 25% decrease in the number of women who would have been recalled (6.9% versus 9.2%).
The AI system was also evaluated with a reader study of five breast radiologists reading the DBT mammograms of 205 women. The area under the curve (AUC) for the standalone AI was 0.84, compared with 0.81 for the average reader (p = 0.002).
The researchers envision their model affecting three different levels upon implementation in a clinical setting: reducing workload and fatigue in radiologists; improving workflow and further clearing the way for DBT in health systems; and reducing unnecessary recalls, stress and radiation exposure for women.
“Future research should include prospective evaluation of our AI model, to assess the percentage of DBT examinations that would be removed from a prospective reading worklist, and to assess how readers perform when interpreting the remaining cases,” the researchers write. “Future research should also evaluate generalizability to multiple DBT manufacturers.”
In an invited commentary piece, Liane Philpotts from Yale University calls for prospective studies to determine how AI’s use will translate into real-world clinical settings, and she also notes that trusting AI could be a challenge for radiologists and patients.
“As radiologists, our relationship with AI will certainly evolve over time. Radiologists need to embrace and help mould the technology that is being developed,” Philpotts writes. “We can only hope continued efforts such as the study by Shoshan et al make progress toward improving both radiologists’ workflow and confidence in interpretation as well as patient outcomes.”
A collaboration of physicists and computer scientists has shown that artificial intelligence (AI) can help control the delicate process of confining an ultra-hot plasma within a fusion reactor. Members of the team say that their demonstration, which exploits a technique known as reinforcement learning to operate the magnetic coils in a tokamak, could enable more speedy development of reactors with novel geometries.
Tokamaks are doughnut-shaped chambers designed to produce energy by fusing light nuclei in the form of a plasma. The nuclei are heated to hundreds of millions of degrees to overcome their mutual repulsion, while the plasma is held in place using the fields from a series of magnetic coils. Those fields keep the plasma away from the chamber’s walls, where it would otherwise lose heat and damage the tokamak.
One aim of fusion scientists is to understand how the spatial distribution of a plasma within the tokamak chamber influences its stability and spatial confinement. This task is complicated by the need to design a new feedback scheme for each configuration, so that the magnets can be tuned appropriately in response to the plasma’s highly nonlinear behaviour. The design process usually involves calculating an initial set of coil currents and voltages, then using a combination of plasma-reconstruction algorithms and feedback controllers to adjust the voltages – and with them the magnetic field. The result is effective control over a plasma’s vertical and radial positions as well as its current, but only with significant effort.
The right rewards
In the latest work, scientists from Google’s London-based DeepMind subsidiary and the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland swapped these multiple feedback controllers for a single controller based on reinforcement learning (RL). An RL algorithm is a form of machine learning that is designed to arrive at an optimum set of output values by adjusting the weights on its nodes in a step-like fashion.
In this case, the algorithmic “agent” receives measured and target values of the plasma parameters – a long list, including numerous spatial dimensions, electrical currents and magnetic fluxes within the tokamak chamber – as its inputs. After processing these values using several layers of nodes, it issues outputs corresponding to the voltage levels on each of the magnets. Once the magnets are adjusted and the new feedback from sensors is received the cycle starts again – being repeated some 10,000 times a second.
This process relies on a computational object known as a reward function, which compares the measured and target values of the plasma parameters at each step and combines the disparity among all parameters into a single value. It is this value that determines how great a “reward” the agent receives for getting closer to the desired values. Conversely, if the plasma ends up crashing into the chamber wall the agent receives a penalty and the process comes to a halt.
Working out this reward function is the first stage of setting up a new RL-based controller, since each function corresponds to a specific plasma configuration. Next, the agent is trained by exposing it to input data from a simulated tokamak, which must realistically describe the plasma’s changing shape and current while limiting its computational demand to keep the learning process manageably short. Finally, the agent’s optimized control scheme is tested on a real tokamak.
Testing the AI
To carry out the experimental stage of the work, the collaboration turned to the EPFL’s Variable-Configuration Tokamak. Initially, members of the team used traditional feedback controllers to create and maintain the plasma in an initial state. At a certain pre-agreed time, they switched to their own control scheme, adjusting 19 separate magnetic coils to tune the plasma so that it ended up with the correct shape and current while keeping the neural network’s weights fixed.
The researchers then showed they could keep control over the plasma’s current and shape – with deviations of no more than a few percent from the intended values – while making the kind of changes needed for a full plasma discharge. They were also able to manipulate the plasma into a variety of shapes, including one similar to that proposed for the ITER reactor being built in the south of France and another known as a snowflake configuration that helps to spread a tokamak’s heat and particle exhaust over a larger surface. In addition, they showed it was possible to set up two separate plasmas within the same tokamak, which they say is a first step to study more advanced plasma configurations.
Improving tokamak performance
The researchers say that their new AI-based scheme could improve tokamak performance, with its open-ended nature perhaps allowing power output to be maximized. More broadly, they say, the technology might lead to new reactor designs by allowing the joint optimization of several device parameters – including plasma shape, wall design and heat load.
Other scientists are enthusiastic about the new work, but caution that its widespread adoption will depend on improving the simulator used to train the AI agent. According to Karel van de Plassche of the Dutch Institute for Fundamental Energy Research and the University of Technology of Eindhoven in the Netherlands, “essential components” of more accurate simulation will include detailed physics on turbulence and magnetohydrodynamics. Ghim Young-chul of the Korea Advanced Institute of Science and Technology (KAIST) notes that it remains to be seen how well the new approach can be applied to tokamaks based on superconductors rather than copper coils, given that the former introduce time delays when regulating current. Another uncertainty, he adds, is the control of stability. While the RL algorithm enables steady-state operation, he notes that “tokamaks have other important unstable events that must be controlled”.
A first-of-its-kind, next-generation research reactor is taking shape on the campus of SCK CEN, the Belgian Nuclear Research Centre in Mol, opening up opportunities for physicists, engineers and technologists to transform an ambitious scientific vision into operational reality over the next 15 years and beyond. With a capital cost of several hundred million Euros, the Multi-purpose hYbrid Research Reactor for High-tech Applications (MYRRHA) represents big science on an ambitious canvas – consisting of a subcritical nuclear reactor driven by a high-power proton linear accelerator, such that the fission reaction is sustained exclusively by the accelerated proton beam (i.e. turning off the proton beam results in immediate and safe shut-down of the reactor).
The implementation of MYRRHA is already under way, with Phase 1 of construction – the so-called MINERVA project – focused on completing the initial section of the proton linac (up to 100 MeV) in 2026. Other MINERVA deliverables include the Proton Target Facility (which will produce radio-isotopes for fundamental physics research and medical applications) and the Full Power Facility (to investigate advanced materials for nuclear fusion). The principal aim in this first phase is to confirm the linac’s reliability in advance of Phase 2 scale-up (due for completion in 2033) to the 400 m long accelerator system that will deliver the 600 MeV proton beam ultimately needed to drive the MYRRHA research reactor. Commissioning of the latter – a Pb-Bi eutectic-cooled and double-walled, unpressurized pool-type reactor with a maximum thermal output of 100 MW – represents the third and final phase of MYRRHA construction and is presently scheduled for 2036.
Here, Hamid Aït Abderrahim, director of MYRRHA and SCK CEN deputy director-general for international affairs, talks to Physics World about the project’s ongoing transition from R&D, demonstration and prototyping into construction and realization.
What does your leadership role involve on the MYRRHA project?
My remit is to ensure that long-term domestic and international financing is in place, while overseeing the design, development and construction effort versus budget and our phased implementation schedule. Externally, I’m responsible for steering MYRRHA’s growing list of strategic partnerships with other big science facilities, while I’m also ultimately accountable for making sure that the core project team – currently around 200 staff at SCK CEN as well as external contractors – has the right mix of skills, experience and specialisms.
Why should early-career scientists and engineers consider MYRRHA as a potential next step in their professional development?
This is an opportunity to shape the delivery and realization of a unique research facility that will address grand societal challenges along several major pathways – from advanced methods to deal with high-level nuclear waste to the at-scale production of medical radioisotopes for the diagnosis and treatment of cancer. At the same time, MYRRHA will enable a diverse research programme in nuclear physics, atomic physics and the study of fundamental interactions, while providing a capability to evaluate next-generation materials with applications in future nuclear fusion reactors. It’s a broad-scope and long-term research endeavour.
How is work progressing with MINERVA, the first phase of the MYRRHA project?
The MINERVA team is overseen by a technical director, with around 85 staff now largely focused on prototyping and realization of the core building blocks for this phase of the project – specifically, the 100 MeV linac, the Proton Target Facility, the Full Power Facility, as well as associated instrumentation and control systems.
Hamid Aït Abderrahim: “Nurturing the talent pipeline will be fundamental to us delivering versus MYRRHA’s long-term project roadmap.”
This team is also working with – and managing – a network of industry contractors on development and installation of a range of auxiliary systems (e.g. radio-frequency cavities, solid-state amplifiers, cryogenics). In parallel, we have around 100 other full-time staff already working on Phase 2 and Phase 3 of MYRRHA, though the emphasis for this group is still skewed towards R&D, design and nuclear licensing and safety studies relating to the reactor.
Presumably the MYRRHA project team will need to scale and adapt over the next five years?
Absolutely. We need constant evolution in terms of our personnel and collective capability – from the initial emphasis on R&D, demonstration and prototyping into the construction and delivery phase of MINERVA. Right now, we’re looking for talented accelerator physicists as well as instrumentation and control experts with experience of linac implementation and operation. We’re also interested in engaging senior designers and mechanical engineers with a background in nuclear reactor technologies and applications.
Equally important, given that MYRRHA is a first-of-a-kind facility, there’s a real desire to support the professional development of our internal experts in key enabling technologies like vacuum, cryogenics, RF systems and high-speed electronics. Nurturing that talent pipeline will be fundamental to us delivering versus MYRRHA’s long-term project roadmap.
So this first-of-a-kind research facility will inevitably require a unique linac capability?
The MYRRHA proton linac is no ordinary linac and will necessitate a fundamental leap forward in accelerator technology. We’re working on game-changing innovations to achieve unprecedented uptime performance – in effect, an almost two orders-of-magnitude improvement versus today’s leading-edge accelerators, yielding continuous-wave proton delivery with almost no tripping out of the main beam. All told, that’s going to mean bulletproof reliability for the accelerator components and subsystems, as well as a fault-tolerant design that exploits twin injectors and, downstream of the injector module, the deployment of ultrafast electronics and dynamic compensation schemes.
How important is collaboration between MYRRHA and other big science laboratories?
We have open and collaborative relationships with a network of large-scale research facilities, sharing specialist domain knowledge and expertise across a range of component and subsystem technologies of mutual interest. Our linac engineers, for example, are in close contact with their counterparts at CERN (Geneva, Switzerland); several CNRS laboratories in France, including IPN Orsay, LPSC, LAL, IPHC and Subatech; IAP (Frankfurt Goethe University) and DESY (Hamburg) in Germany; and the European Spallation Source (Lund, Sweden).
Outside Europe, we have initiated joint development projects with the likes of the Spallation Neutron Source (Oak Ridge, Tennessee, US), TRIUMF (Vancouver, Canada) and J-PARC (Tokai, Japan). These collaborations are a win-win in terms of the partners’ overall productivity and fundamental to the successful delivery of MINERVA in the near term and MYRRHA over the long term.
Call for applications: the MYRRHA management team is currently recruiting for a number of positions to support the design, development and construction of the project’s proton linear accelerator. Open vacancies include RF engineer/RF physicist; power converter engineer; accelerator integrator; and embedded systems engineer for particle accelerator applications. Other profiles of interest include nuclear engineers, mechanical engineers, nuclear safety experts, project management engineers with knowledge of nuclear safety, as well as research scientists specializing in heavy liquid metals (Pb or Pb-Bi).
MYRRHA: the view from the project team
Open, warm, cosmopolitan: that’s how Alexander Denisov, project manager for the MYRRHA target facilities, describes the working environment at SCK CEN. “Inclusivity is key here,” says Denisov. “After all, the MYRRHA project team comprises scientists, engineers and other specialists from across the EU, Eastern Europe, UK, Africa, Asia and North America. It’s very much a cross-disciplinary and multicultural melting pot.”
Equally important, especially for young scientists and engineers, is the opportunity that MYRRHA presents to do unique and rewarding work. “The MYRRHA project is a trail-blazer in many ways,” he adds, “so talented scientists and engineers are well positioned as they seek to establish and build their professional reputation.”
As with all big science initiatives, collaboration is hard-wired into MYRRHA’s collective DNA. Early-career researchers and engineers, for example, are often required to engage directly with the project’s scientific advisory boards as well as MYRRHA’s scientific partners (the likes of CERN, TRIUMF and ESS) and the facility’s nascent community of research users.
“We’re well funded and moving fast towards our near-term goal of delivering MINERVA by the end of 2026,” notes Denisov. “For sure, MYRRHA team members will be able to tackle all sorts of challenges – across R&D, design, construction, commissioning and acceptance – that they will not encounter anywhere else.”
For Karolien Saenen, who coordinates the building design and associated infrastructure for MINERVA’s scientific systems, it is the diversity of interactions on the project that is especially exciting – if sometimes challenging. “I need to work with multiple cross-disciplinary teams spanning research, engineering, project management and infrastructure,” she explains. “It’s a warm and welcoming community, though – a real collective effort where everyone is aligned and pulling in the same direction.”
Mention “nuclear power” and attention almost immediately turns to safety. Despite huge advances in nuclear technology in recent decades, everyone still thinks about the accidents that occurred at older reactors like Chernobyl, Three Mile Island or Fukushima. Safety – and the politics surrounding it – remains the single biggest issue influencing the development of nuclear power around the world.
Dozens of countries don’t even have – or don’t want – nuclear power. Some have nuclear but are phasing it out. Germany, for example, closed three of its six remaining nuclear plants on 31 December 2021, which together accounted for 6% of the country’s electricity. The other three will shut down later this year, with much of the shortfall in the short term being made up by burning natural gas.
A lot of attention is turning to smaller and potentially safer “modular” reactors that are, in principle, quicker and cheaper to build.
For many, however, nuclear power is starting to look like an acceptable solution to reach net zero. According to the International Atomic Energy Agency (IAEA), there are currently 443 nuclear fission plants operating around the world, with a further 50 under construction in 19 countries. Most of these reactors are “big nuclear” plants producing more than 1 gigawatt of electricity (GWe), each taking decades and billions of dollars to build.
However, fission is a very scalable technology and a lot of attention is turning to smaller and potentially safer “modular” reactors that are, in principle, quicker and cheaper to build. So could these reactors, which are defined as having a typical output of 300 MWe, be part of the answer to delivering carbon-free energy to meet the doubling of demand that is predicted in coming years?
A burgeoning market
According to market-research firm Allied Market Research, the world-wide market for small modular reactors (SMRs) was worth $3.5bn in 2020 and is projected to reach $18.8bn by the end of the decade. Apart from being small and cheap, the big advantage of SMRs is that they are designed to be built in factories and then transported in modules to sites for installation. Here in the UK, the government has already earmarked up to £215m for SMRs as part of a larger Advanced Nuclear Fund to invest in the next generation of nuclear.
One firm getting in on the act is Rolls-Royce, which last November said it was setting up the Rolls-Royce Small Modular Reactor (RR-SMR) business unit, following a £195m cash injection from private firms and a £210m government grant. Costing about £2bn, each of its 470 MWe SMRs would be able to power a million homes. Rolls-Royce sees the approach as low risk as light-water reactors are a mature technology with a proven track record.
In fact, SMRs have a decent and predictable LCOE (levelized cost of electricity) value, which is a measure of the average net cost, in today’s money, of generating electricity from a plant over its entire lifetime. LCOEs are used for investment-planning purposes to compare different methods of electricity generation on a consistent basis. If approved for use in the UK, Rolls-Royce could build up to 16 reactors, generating £250bn in export sales. The programme could create 40,000 new jobs by 2050.
In addition to providing a stable, base load of power, SMRs would give us the energy to make “green” hydrogen.
In addition to providing a stable, base load of power, SMRs would give us the energy to make “green” hydrogen, thereby supporting the path to net-zero and the decarbonization of transport. But SMRs are just one part of a wider programme of advanced nuclear reactors. Indeed, the IAEA has a database of 72 different designs. Some are hugely innovative using advanced fuels, breeder technology and various cooling strategies to slash construction and operation costs, while addressing safety and non-proliferation issues.
Powerful stuff
Over in the US, TerraPower, a start-up co-founded in 2008 by Bill Gates, has chosen Kemmerer – a former coal town in Wyoming – as the preferred site for its new “Natrium” fission reactor. It would use liquid sodium both to cool the reactor and store energy. With a power output of 345 MWe that can be boosted during peak demand to 500 MWe, a prototype could be complete by 2028. The company ultimately hopes to sell its reactors for $1bn a pop.
TerraPower is also working on “travelling wave reactor” (TWR) technology. This proposed fission reactor would convert fertile material (in the reactor) into usable fissile fuel, while at the same time burning up any unwanted fissile material. TWRs use fuel efficiently without high levels of uranium enrichment or reprocessing, instead directly using depleted uranium, natural uranium or even, potentially, spent fuel.
There are even ultra-compact, “micro-reactors”, some of which could be transported on a truck.
The concept is still being developed – no TWRs have ever been built. But to me it’s an exciting prospect. TerraPower claims its TWR could use mined uranium 30 times more efficiently. And with all the fuel staying in the reactor until it’s used up, the firm says its technology has none of the safety and proliferation concerns that arise with reprocessing used fuel. Given existing global stockpiles of depleted uranium, TerraPower reckons that its TWRs could power the planet for at least a thousand years.
There are even ultra-compact, “micro-reactors” being designed with outputs of 1–20 MWe, some of which could be transported on a truck. These new designs include the U-Battery from Urenco and partners as well as the eVinci by Westinghouse. They could be used, say, to produce heat (for industrial applications like steel making), to power remote communities, to serve as back-up for the main electricity grid or even to help disaster-relief efforts.
The speed at which any of these technologies are developed will, of course, be slowed by essential safety regulations and uncertain market demand. The usual approach taken by start-up companies – build your best prototype and then see what happens – isn’t feasible with nuclear as mistakes are likely to be expensive, long-lasting and damaging for the environment. But with the right regulatory approach, SMRs could be a key part of the global net-zero plan, delivering the carbon-free power we so desperately need.
In this episode of the Physics World Weekly podcast I chat with three physicists about a room-temperature time crystal that they have created. Hossein Taheri at the University of California at Riverside, Andrey Matsko from NASA’s Jet Propulsion Laboratory and Krzysztof Sacha at the Jagiellonian University in Poland also explain the physics behind time crystals and how they could be used in practical applications.
Also in the podcast is Pradeep Niroula of the University of Maryland, who has written an article for Physics World called “Conquering the challenge of quantum optimization”. He explains how optimization algorithms runing on quantum computers could simulate quantum systems such as molecules, and even improve pizza delivery.
Physics World’s Laura Hiscott also joins me for a chat about the Physics World Careers 2022 guide, which has just been published. It is chock full of valuable information for physics students and graduates who are embarking on their careers or fancy a change in what they are currently doing. This year’s guide looks at employment opportunities in burgeoning areas such as quantum computing and explains how to get the most out of a summer work placement.
